The present invention relates to an improved process for synthesizing organic compounds for use as bleach activators.
The synthesis of ingredients for use in low unit cost consumer goods such as laundry detergents, fabric softeners, and the like is of considerable interest to manufacturers. Indeed, the low cost synthesis of ingredients is typically the rate limiting step in the course of bringing a consumer product to the market. Due to the large number of ingredients in consumer goods such as laundry detergents, the expense of individual ingredients must be minimized in order to keep the cumulative product cost within acceptable ranges. The expense associated with the manufacture of consumer goods ingredients is often due to either the cost of the raw materials used to make such ingredients or to the complex reaction and processing chemistry which is required in their manufacture. Accordingly, manufacturers conduct a continuing search for both inexpensive raw materials or simplified reaction sequences.
Amido acid phenyl ester sulfonates form a class of materials which can serve as bleach activators in laundry detergents and other types of bleach-containing cleaning compositions. Such activators have several desirable attributes including excellent bleaching performance with minimal color damage on fabrics dyes, good washing machine compatibility and a good odor profile in the wash. While these materials are potentially obtainable from inexpensive raw materials, the synthesis is somewhat complicated and typically involves the use of solvents. Problems can also arise in the formation of color impurities, caused by the reaction of color forming bodies, in the end product. These color forming impurities or bodies result in a finished product which is undesirable to consumers and consequently unusable because of its appearance. This results in additional steps to remove the colored impurities. These additional steps have the problem that not only do they remove the colored impurities, add additional time and cost, but they also remove some of the amido acid phenyl ester sulfonates along with the colored impurities. Thus, the synthesis of amido acid phenyl ester sulfonates is not straightforward and can be surprisingly problematic.
Accordingly, the need remains for a simple, inexpensive yet effective process for the production of amido acid phenyl ester sulfonates which does not result in the formation of colored impurities in the final product.
U.S. Pat. Nos. 5,466,840, 5,391,780, 5,393,901, 5,393,905, 5,523,434, 5,391,780, 5,414,099, 5,534,642, 5,153,541, 5,650,527, 5,286,879 and 5,523,434.
This need is met by the present invention, wherein improved process for preparing a purified amido acid phenyl ester sulfonate are provided.
According to a first aspect of the present invention, a process for the preparation a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate is provided. The process comprises the steps of:
reacting an acetoxy benzene sulfonate salt with a high purity amido carboxylic acid, wherein said high purity amido carboxylic acid comprises least about 90%, preferably about 95%, even more preferably about 97% by weight, of a amido carboxylic acid of the formula: 
xe2x80x83wherein R is C5-C21 hydrocarbyl, R1 is selected from hydrogen and C1-C3 alkyl, and n is an integer from about 1 to about 8; and less than about 10% by weight, of color forming bodies;
wherein the process is performed in the presence of less than about 10 ppm, preferably less than about 5 ppm, more preferably less than about 2 ppm, even more preferably less than about 0.5 ppm of transition metals, preferably selected from the group consisting of iron, nickel, chromium and mixtures thereof, more preferably iron, nickel, and mixtures thereof
According to a second aspect of the present invention, the process for preparing a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate comprising the steps of:
(a) reacting a high purity amido carboxylic acid, wherein said high purity amido carboxylic acid comprises least about 90%, preferably about 95%, even more preferably about 97% by weight, of an amido carboxylic acid of the formula: 
xe2x80x83wherein R is C5-C21 hydrocarbyl, R1 is selected from hydrogen and C1-C3 alkyl, and n is an integer from about 1 to about 8, M is H or an alkali metal salt; and less than about 10% by weight of color forming bodies;
xe2x80x83wherein the process is performed in the presence of less than about 10 ppm, preferably less than about 5 ppm, more preferably less than about 2 ppm, even more preferably less than about 0.5 ppm of transition metals, preferably selected from the group consisting of iron, nickel, chromium and mixtures thereof, more preferably iron, nickel, and mixtures thereof, with an acid halide to prepare the corresponding amido acid halide; and
(b) reacting the amido acid chloride of step (a) with a phenolsulfonate salt.
According to a third aspect to provide 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate when prepared according to either the first or second aspect of the present invention.
According to a fourth aspect to provide cleaning compositions comprising 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate prepared according to either the first or second aspect of the present invention.
Accordingly, it is an aspect of the present invention to provide a process for preparing a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate. It is yet another aspect of the present invention to provide flexibility to a process for preparing a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate. These, and other aspects, features and advantages of the present invention will be recognizable to one of ordinary skill in the art from the following description and the appended claims.
All percentages, ratios and proportions herein are on a weight basis unless otherwise indicated. All documents cited herein are hereby incorporated by reference.
The process of the present invention for preparing amido acid phenyl ester sulfonates involves as an important feature limiting the amount of transition metals and color forming bodies present in the process. As earlier noted, it is the reduction of the transition metals and color forming bodies content in the process which leads to the benefits and advantages of the present invention.
According to a first aspect of the present invention, a process for the preparation a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate is provided. The process comprises the steps of:
reacting an acetoxy benzene sulfonate salt with a high purity amido carboxylic acid, wherein said high purity amido carboxylic acid comprises least about 90%, preferably about 95%, even more preferably about 97% by weight, of a amido carboxylic acid of the formula: 
xe2x80x83wherein R is C5-C21 hydrocarbyl, preferably C5-C14 hydrocarbyl, more preferably C6-C12 alkyl, C6-C12 alkenyl, even more preferably C6-C10 alkyl, R1 is selected from hydrogen and C1-C3 alkyl, preferably H, methyl, more preferably methyl, and n is an integer from about 1 to about 8; preferably an integer from about 2 to about 7, more preferably an integer from about 3 to about 6 and less than about 10%, preferably less than about 5%, more preferably less than about 2%, even more preferably less than about 1% by weight, of color forming bodies;
wherein the process is performed in the presence of less than about 10 ppm, preferably less than about 5 ppm, more preferably less than about 2 ppm, even more preferably less than about 0.5 ppm of transition metals, preferably selected from the group consisting of iron, nickel, chromium and mixtures thereof, more preferably iron, nickel, and mixtures thereof.
It is preferred that the high purity amido carboxylic acid comprises least about 95%, more preferably 97%, of a amido carboxylic acid of the formula: 
The total impurities indicated above negatively influence the ability to effectively recrystallize the product due to the impurities drawing product into the filtrate/centrate by serving as hydrotropes. In addition, it is important to have less than 1%, less than 0.5%, less than 0.1% of total aminoalkanoic acid and cyclic lactam.
Preferably, the high purity amido carboxylic acid is produced by the reaction of a carboxylic acid of the formula: 
wherein R is C5-C21 hydrocarbyl; with a lactam of the formula: 
wherein R1 is selected from hydrogen and C1-C3 alkyl, and n is an integer from 1 to 8. Suitable lactam monomers include butyrolactam, valerolactam, epsilon-caprolactam, beta propiolactam, delta valerolactam, and similar lactams. These lactams may be substituted at the nitrogen atom by hydrocarbon radicals containing one to three carbon atoms, for example, methylcaprolactam. Epsilon-caprolactam and suitable derivatives thereof are the preferred lactam monomers.
The carboxylic acid contains an aliphatic, such as a straight or branched chain, or aliphatic radical, cycloaliphatic or hydroaromatic radical. The carboxylic acid has from about 6 to about 22 carbon atoms, preferably about 8 to about 20 carbon atoms, and most preferably from about 7 to about 10 carbon atoms. These radicals may be connected to the carboxyl group through an aromatic radical. The carboxylic acids may be straight or branched chain fatty acids of natural or synthetic origin which may be of a saturated or unsaturated nature. The carboxylic acids may be used in pure form or else in the form of their mixtures.
Suitable examples of carboxylic acids and esters are: Caprylic acid, methyl caprylate, pelargonic acid, methyl pelargonate, capric acid, methyl caprate, isopropyl caprate, undecylic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, behenic acid, teraphthalic acid, dimethyl teraphthalate, phthalic, isophthalic acid, napthene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclo-hexanediacetic acid, diphenyl-4,4xe2x80x2-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Preferred carboxylic acids are capric and capryltic.
Preferably, the process is performed in the presence of a polar aprotic reaction solvent such as dialkylacetamides, such as, N,N-dimethylacetamide; dialkyl sulfoxide wherein the alkyl group has one to six carbon atoms such as dimethyl sulfoxide; dimethyl ethers of diethylene glycol such as triglyme; cyclic or acyclic alkyl sulfones wherein the alkyl group has one to six carbon atoms such as tetrahydrothiophene-1,1-dioxide; and halogenated aromatic solvents such as dichlorobenzene and trichlorobenzene; and alkyl substituted aromatic solvents where the alkyl groups contain one to six carbon atoms such as triisopropylbenzene. Preferably, the reaction solvent is tetrahydrothiophene-1,1-dioxide.
It is preferred that the process is conducted at a temperature of from about 120xc2x0 C. to about 220xc2x0 C.
Preferably the process may contain a transesterification catalysts. Such catalysts include tertiary amine catalysts, alkali metal salts, metallic catalysts, acidic catalysts, and combinations thereof. Specific examples of catalysts for use in the present invention include: dimethyl aminopyridine, imidazole, sodium acetate, sodium hydroxide, and titanium tetraisopropoxide. The transesterification catalyst(s) is added in an amount of about 0.01 to about 0.3 mole, preferably about 0.1 to about 0.3 mole equivalent of the acetoxy benzene sulfonate salt.
The process for preparing a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate by reacting an acetoxy benzene sulfonate salt with a high purity amido carboxylic acid preferably comprises the steps of:
(a) reacting an alkali metal salt of 4-hydroxybenzene sulfonic acid with a C2 to C4 carboxylic anhydride at a sufficient temperature and time in a reaction solvent to form a reaction mixture having an alkali metal salt of 4-acyloxybenzenesulfonic acid and a C2 to C4 carboxylic acid, wherein the alkali metal salt of 4 hydroxybenezene sulfonic acid and C2 to C4 carboxylic anhydride are present in a mole ratio of 1:1 to 1:40, respectively, and the reaction solvent is present in a weight ratio of 1:1 to 20:1 based on the weight of the alkali metal salt of 4-hydroxybenzene sulfonic acid, provided that excess carboxylic anhydride is removed under reduced pressure from the reaction vessel;
(b) adding a [(1-oxyalkanoyl)amino]alkanoic acid and at least one transesterification catalyst to said reaction mixture and heating at a temperature of from about 120xc2x0 C. to about 220xc2x0 C. for from about 0.5 to about 10 hours and a pressure sufficient to maintain reflux of said reaction solvent and to remove the C2 to C4 carboxylic acid from the reaction vessel, to form a reaction product containing a salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate wherein the moles of the [(1-oxyalkanoyl)amino]alkanoic acid added is 0.7 to 5 times the moles of the alkali metal salt of 4-hydroxybenzene sulfonic acid;
(c) admixing said reaction product including reaction solvent and a salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate with a water-based purification system to form a purification mixture, said water-based purification system including a processing aid and having water present at a ratio of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate to water ranging from about 1:0.05 to about 1:50;
(d) separating a purified salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate from said purification mixture; and
(e) collecting the salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate.
The preparation of the 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate according to the second aspect involves two basic steps and is fully described in U.S. Pat. No. 5,466,840, the disclosure of which is herein incorporated by reference. In the first step, a salt, such as an alkali metal salt, of 4-hydroxybenzenesulfonic acid is reacted with a C2 to C4 carboxylic anhydride preferably at a temperature of 50xc2x0 C. to 200xc2x0 C. for 0.5 to 5 hours in a reaction solvent to form a reaction mixture having a salt of 4-acyloxybenzenesulfonic acid and a C2 to C4 carboxylic acid. Preferably, the reaction is conducted at a temperature of 110xc2x0 C. to 170xc2x0 C. for 1 to 2 hours. Preferably, the salt is an alkali metal salt and may be any alkali metal such as sodium and potassium, or alternatively another salt such as calcium, magnesium or ammonium. However, sodium is the most preferred.
Preferably, when present, the C2 to C4 carboxylic anhydride is present in an amount of from about 1 to about 40 moles per mole of the salt of 4-hydroxybenzenesulfonic acid, preferably about 1 to about 5 moles, and most preferably about 1 to about 1.3 moles. Examples of suitable C2 to C4 carboxylic anhydrides are acetic anhydride, propionic anhydride, butyric anhydride, and isobutyric anhydride with acetic anhydride being the most preferred.
Preferably, when the process involves the reaction of an alkali metal salt of 4-hydroxybenzene sulfonic acid with a C2 to C4 carboxylic anhydride, namely the second aspect of the present invention, the reaction solvent is present in a ratio of reaction solvent to the salt of 4-hydroxybenzenesulfonic acid of about 1:1 to about 20:1, preferably about 4:1 to about 6:1 weight ratio.
A processing aide may be added to the water-based purification system to, among other reasons, enhance separation and reduce foaming in the process. The processing aide is selected from the group consisting of linear or branched C1 to C6 alcohols or diols, linear or branched C1 to C6 ketones, linear or branched C1 to C6 acids, linear or branched C1 to C6 esters, cyclic or acyclic C1 to C6 ethers, linear or branched, cyclic or acyclic C1 to C6 sulfoxides and sulfones and mixtures thereof. Most preferably, the processing aide is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, acetone, acetic acid and mixtures thereof with isopropyl alcohol being the most preferred.
Upon completion of the transesterification reaction and the formation of the salt of 4-sulfophenyl-[(1oxyalkanoyl)amino]alkanoate, the reaction solvent may be removed in an optional step. The removal of solvent is accomplished by either an evaporative process such as distillation or drying, or by crystallization followed by filtration. Removal of the solvent is conducted at low vacuum and at a temperature at which vaporization of the solvent occurs. Preferably, the vacuum range is from about 0.5 absolute to about 100 mm Hg, and the temperature range is from about 100xc2x0 C. to about 230xc2x0 C. The upper end of the temperature range has the advantage of more rapid solvent removal, whereas the lower end of the temperature range has the advantage of reducing high temperature-promoted product decomposition and the associated increase in color and impurities. Preferably, at least about 90% and more preferably at least about 95% of the solvent is removed. Of course, it is important to note that this removal of solvent is entirely optional in the present invention as the water-based purification system may operate in the presence of large amounts of reaction solvent.
Removal of the co-carboxylic acid can be achieved via distillation or by sparging with an inert gas such as nitrogen. Additional reaction solvent may be added in the transesterification step to maintain a fluid reaction mixture . The moles of [(1-oxyalkanoyl)amino alkanoic acid added is about 0.7 to about 5 times the moles of the salt of 4-hydroxybenzenesulfonic acid used in the first step.
The [(1-oxyalkanoyl)amino alkanoic acid is prepared by routes which are well known in the art and disclosed for example in U.S. Pat. Nos. 5,391,780; 5,414,099; 5,534,642; 5,153,541; 5,650,527; 5,286,879 and 5,523,434, the disclosures of which are herein incorporated by reference. A preferred synthesis for the [(1-oxyalkanoyl)amino alkanoic acid is an amidation reaction involving reacting a nitrogen compound selected from a lactam and an amino acid with a carboxylic acid or ester. Preferably, the [(1-oxyalkanoyl)amino alkanoic acid is 6-[(1-oxyoctyl)amino hexanoic acid, 6-[(1-oxynonyl)amino hexanoic acid, 6-[(1-oxydecyl)amino hexanoic acid or mixtures of the three.
The reaction product including the salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate is admixed with a water-based purification system to yield the purified salt of the present invention. The water-based purification system, of course, includes at least a minimum amount of water. However, other ingredients such as processing aids may be included in the system.
The water-based purification system has a minimum amount of water such that the ratio of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate to water ranges from about 1:0.05 to about 1:50. More preferably, the ratio of salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate to water ranges from about 1:0.1 to about 1:40. As discussed earlier, the reaction solvent does not need to be removed from the reaction product of the salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate synthesis. In such instances, wherein at least about 10%, and more preferably at least about 20% and more preferably at least about 40% of the reaction solvent remains, a lower amount of water is required in the system. In such cases, the ratio of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate to water preferably ranges from about 1:0.1 to about 1:40. When the reaction solvent is optionally removed as described hereinbefore, a larger percentage of water may be necessary in the purification system. In such instances, the ratio of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate to water ranges from about 1:1 to about 1:50.
In highly preferred scenarios, the processing aide is miscible with water and has a density of less than or equal to the preferred reaction solvent, tetrahydrothiophene-1,1-dioxide so as to increase the density difference between the product salt and the purification system thereby increasing the ease of removal of the salt. The solvent tetrahydrothiophene-1,1-dioxide has a density of 1.216 gm/cm3. The processing aide is typically present in the purification system at a ratio of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate to processing aide ranging from about 1:0.1 to about 1:50 and most preferably from about 1:1 to about 1:20. The amount of processing aide employed is mainly dependent on the physical properties desired. The lower end can be chosen to minimize foaming (although less is also needed when reaction solvent which also reduces foaming is present). The upper end is typically chosen for convenience during product recovery such as filtering or centrifuging. When a processing aide is used in conjunction with the water-based purification system, product yields from recrystallization are typically greater than about 75%, more preferably 85%, and most preferably 90%.
As discussed earlier, the water-based purification system provides increased flexibility to the prior art processes by allowing recovery of product salt from either a slurry or a homogeneous solution. That is, in a typical process the step of admixing reaction product salt with the purification system with or without processing aide as described hereinbefore yields either a slurry or homogeneous solution of formed product salt. The purification may be conducted on this slurry or homogeneous solution at room or slightly elevated temperatures to remove impurities and color forming bodies. However, the admixing step may also in optional embodiments involve heating the admixture from about 30xc2x0 C. to about 100xc2x0 C. to form a slurry or homogenous solution of product salt. The product salt may then be recovered from this homogenous solution or slurry to yield a highly purified product salt. The use of a homogenous solution or slurry provides flexibility and a controlled recrystallization of the product salt to impart various desired results.
The next step of the process involves the separation of the purified salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate from the water-based purification system and any remaining solvent. This separation may be accomplished by methods which are well-known in the art such as centrifugation or filtration. The filtrate from this separation step may include reaction solvent, water and processing aides, if present, which can be individually recovered and recycled to their respective steps. If desired, the purified salt may be dried by any conventional drying technique such as a ring drier or vacuum oven. It is important to note that the purification with the water-based system and separation of the product may be repeated as necessary until a salt of 4-sulfophenyl-[(1- oxyalkanoyl)amino]alkanoate of the desired purity is obtained. Depending upon the purity of the starting materials, greater than about 80% and preferably about 90% yield of product may be obtained in the process of the present invention.
The processes as described herein may be conducted stepwise as a batch process or on a continuous basis. The salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate product, preferably, has the general formula RC(O)N(R1)(CH2)nC(O)xe2x80x94OBS where R represents C5-C21 alkyl, C5-C21 alkenyl, R1 represents hydrogen or methyl; n is an integer from about 1 to about 8; and xe2x80x94OBS is an oxybenzenesulfonate leaving group. Preferably, the purified salt of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate is sodium 4-sulfophenyl-6-[(1-oxynonyl)amino]hexanoate, wherein R is C8H17, n is 5 and or sodium 4-sulfophenyl-6-[(1-oxydecyl)amino]hexanoate wherein R is C9H19, n is 5. The product may also include mixtures of compounds.
According to a second aspect of the present invention, the process for preparing a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate comprises the steps of:
(a) reacting a high purity amido carboxylic acid, wherein said high purity amido carboxylic acid comprises least about 90% ,preferably about 95%, even more preferably about 97% by weight, of an amido carboxylic acid of the formula: 
xe2x80x83wherein R is C5-C21 hydrocarbyl, preferably C5-C14 hydrocarbyl, more preferably C6-C12 alkyl, C6-C12 alkenyl, even more preferably C6-C10 alkyl, R1 is selected from hydrogen and C1-C3 alkyl, preferably H, methyl, more preferably methyl, and n is an integer from about 1 to about 8; preferably an integer from about 2 to about 7, more preferably an integer from about 3 to about 6, M is H or an alkali metal salt; and less than about 10%, preferably less than about 5%, more preferably less than about 2%, even more preferably less than about 1% by weight of color forming bodies;
xe2x80x83wherein said process is performed in the presence of less than about 10 ppm, preferably less than about 5 ppm, more preferably less than about 2 ppm, even more preferably less than about 0.5 ppm of transition metals, preferably selected from the group consisting of iron, nickel, chromium and mixtures thereof, more preferably iron, nickel, and mixtures thereof; and
(b) reacting the amido acid chloride of step (a) with a phenolsulfonate salt. Preferably the high purity amido carboxylic acid comprises least about 95%, of a amido carboxylic acid of the formula: 
The process according to the second aspect of the invention can be conducted in the presence of water or in the absence of water. Preferably, when the process is conducted in the presence of water it is conducted in a two-phase reaction medium comprising water and an organic solvent which is compatible with the amido acid halide formed in step (a). Alternatively the process may be conducted in the presence of an organic solvent which is compatible with the amido acid halide formed in step (a).
Preferably the acid halide is an inorganic acid halide selected from the group consisting of PCl3, PCl5, POCl3, and their corresponding bromides, or oxalyl chloride, more preferably the acid halide is SOCl2, PCl3, PCl5, POCl3, even more preferably SOCl2. It is preferred that the acid halide be present in the process at about greater than or equal to 1 mole equivalent.
Color Forming Bodies
It has now been surprisingly found that a high purity amido acid phenyl ester sulfonates can be formed with minimal, preferably free of, colored impurities. There are several key aspects to minimizing the formation of colored impurities in the final product. They are (i) minimizing the amount of color forming bodies in the starting materials; (ii) minimizing the amount of transition metals present in the reaction; (iii) using high purity amido carboxylic acid; (iv) minimizing amount of oxygen present in the synthesis of starting materials and products; (v) minimizing exposure of amido carboxylic acid to high temperature; and (vi) minimizing exposure of final product to high temperatures when solvent concentration is low (concentration less than about 1:1 ratio of sulfolane to product). All six or any possible combinations thereof of these conditions can produce a final crude product of acceptable color.
(i) Minimizing the Amount of Color Forming Bodiesxe2x80x94In the present invention there is less than about 10%, preferably less than about 5%, more preferably less than about 2%, even more preferably less than about 1%, by weight of color forming bodies present in the starting materials. These color forming bodies are believed to be amido acid which has decomposed or is the product of some side reaction produced during the formation of the amido acid. It is believed, while not wishing to be limited by theory, that both intramolecular and intermolecular decomposition of the amido carboxylic acid result in the formation of the color forming bodies. The intramolecular mechanism decomposition is believed to result in formation of caprolactam and nonanoic acid, while intermolecular mechanism decomposition is believed to result in formation of 6-aminocaproic acid and amido acid oligomers. One possible mechanism for color formation is: 
(ii) Minimizing the Amount of Transition Metalxe2x80x94The process of the present invention is performed in the presence of less than about 10 ppm, preferably less than about 5 ppm, more preferably less than about 2 ppm, even more preferably less than about 0.5 ppm of transition metals, preferably selected from the group consisting of iron, nickel, chromium and mixtures thereof, more preferably iron, nickel, and mixtures thereof. It has now been found that even trace amounts, i.e. greater than 10 ppm of transition metal, can result in a product with a poor color, because of increased formation of color forming bodies by the transition metal. Additionally, when oxygen is present in combination with a transition metal, such as iron or nickel, a product is formed with even worse color than the product formed with just transition metal present. The transition metal is believed to act as a catalyst, optionally in combination with oxygen, in the breakdown of the amido acid to form the color forming bodies. That is, one possible mechanism, where the transition metal is, for, example iron is: 
By transition metal, it is meant that all possible oxidation states of transition metals are included, for example Fe2+ and Fe3+.
There are many possible ways or reducing and even eliminating transition metals from the present process. Examples include minimizing the contact of the reaction with transition metals such as, by the use of glass line reactors, recrystallizing the high purity amido carboxylic acid, transferring the high purity amido carboxylic acid as a solid, using distilled material immediately rather than storing in metal tanks, and the use of chelants.
(iii) High Purity Amido Carboxylic Acidxe2x80x94The process of the present invention is performed using a high purity amido carboxylic acid which comprises least about 90%, preferably about 95%, even more preferably about 97% by weight, of a amido carboxylic acid of the formula: 
wherein R is C5-C21 hydrocarbyl, R1 is selected from hydrogen and C1-C3 alkyl, and n is an integer from about 1 to about 8. The use of amido carboxylic acid other that high purity amido carboxylic acid results in the formation of a product with poor color. When the amido carboxylic acid is kept molten for extended (or even modest or short) periods of time, the rate at which these color bodies form is greatly increased. It is believed that heat increases the following reaction: 
as well as the reaction which forms the aminoalkanoic acid and cyclic lactam.
Also, slow decomposition of amido acid to fatty acid, lactam and 6-aminocaproic acid adds to the possibility of further color bodies forming over time. Darker crude product requires more water to remove color (if it can be removed), and may require additional purification steps, both of which lead to increased product loss to the filtrate. Consequently, it is preferred to minimize the time that the amido carboxylic acid is heated and or remains molten. A diluent can also be used to decrease the melting point of the amido carboxylic acid. Such diluents may include solvents such as sulfolane or acetic acid.
When necessary recrystalization can be done on the crude amido carboxylic acid. Recrystallization of the amido acid with a solvent such as, an alcohol solvent with or without water, leads to amido carboxylic acid of sufficient purity to be suitable for use in the production of 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate. While not wishing to be limited by theory it is believed that the recrystalization reduces the amount of cyclic lactam and aminoalkanoic acid to be  less than 1.0%. However, it is preferred to prepare a amido carboxylic acid which does not require any further purification steps and will produce a 4-sulfophenyl-[(1-oxyalkanoyl)amino]alkanoate of acceptable purity and color.
(iv) Minimizing the Amount of Oxygenxe2x80x94The process of the present invention is performed keeping the level of residual oxygen at a minimum. Minimizing oxygen is accomplished by use of vacuum, inert gas blanket or sparge. If oxygen is present in the storage of the reagents and/or in the synthesis of the bleach activator color formation is probable. Low oxygen levels slow the color formation process, especially in the absence of transition metals such as iron or nickel.
(v) Minimizing exposure of amido carboxylic acid to high temperaturexe2x80x94Even in the absence of transition metals and oxygen, the amido carboxylic acid can undergo decomposition if exposed to high temperatures. For instance the purity of recrystallized amido carboxylic acid is reduced from 97.7% to 83.9% in only 3 hours at 165xc2x0 C. and down to 39.5% in 18 h. Decomposition at a rate of about 1% per day is also observed at temperatures below 100xc2x0 C., even in the presence of an argon atmosphere. As mentioned earlier, air exposure as well as the presence of transition metals does increase color formation. Overall, temperature, time and air all play a key role in color formation.
Typically, the solid amido acid will be stored at room temperature, to minimize the exposure of the amido acid to high temperature. If necessary the solid could be kept at higher temperature, about 70xc2x0 C., if there was a reason to do so with minimal decomposition. If stored in molten form (for convenience associated with pumping, etc.) then the decomposition of the amido carboxylic acid will occur over time. Other factors such as, purity of material, transition metal content, exposure to air/oxygen, etc., become significant. For example, the color of the amido acid does not change noticeably in 3 hours at 105xc2x0 C. if the molten amido acid is stored under an argon blanket. If exposed to air at this temperature the color formation is obvious in 3 hours. Regardless, both the amido acid kept under argon and that kept under argon and exposed to air produce a final product with an unacceptable color. At some point the color forming bodies formed in 3 hours at 105xc2x0 C under the argon blanket will result in real color in the final crude product. Even without exposure to air, color bodies do form when the acid is kept molten for prolonged periods of time. For this is the reason it is preferred to store the amido acid as a solid or minimizing time under molten conditions. Furthermore, it may be the case that any time spent in the molten form is harmful to the final product color.
If necessary storage of the molten material is possible, but the material must be kept molten at a lower temperature, such as 85xc2x0 C. This will result in much less apparent decomposition, typically a loss of activity much less than 1% per day or even per week. However, it is believed that this low temperature molten material will accumulate color forming bodies if not properly cared for. That is minimizing the transition metal content, and oxygen content, etc. A small amount of aminoalkanoic acid can produce a significant amount of forming color bodies.
One possible intermolecular mechanism for the formation of nonanoic acid, amido acid dimers and consequently to color forming bodies: 
OR another possible mechanism for the generation of 6-aminocaproic acid and caprolactam via intramolecular mechanism and consequently to color forming bodies. 
(vi) Minimizing exposure of final product to high temperatures when solvent concentration is lowxe2x80x94(concentration less than about 1:1 ratio of sulfolane to product). This is important when trying to remove solvent from product (if water purification method not utilized). Decomposition and color formation can reach several percent per hour at temperatures above 190 deg C., particularly under high vacuum and when exposed to air.
Intermolecular Mechanism 
OR another possible mechanism for the generation of 6-aminocaproic acid and caprolactam.
Intramolecular Mechanism 
It is also worth noting that some of the possible byproducts are activators in there own right. For example: 
However as it is believed that these byproducts are intermediates in the production of the color forming bodies, it is preferred to not only minimize their content in the intermediates and product, but also to minimize their formation.
The process of the present invention will be further illustrated by a consideration of the following examples, which are intended to be exemplary of the invention.